#include<stdio.h>
#include<iostream>
#include<string.h>
using namespace std;
int main()
{
	int i, a, b, c;
	float sum = 0;
	cin >> a >> b >> c;
	sum += (1 + a) * a / 2;
	for (i = 1; i <= b; i++)sum += i * i;
	for (i = 1; i <= c; i++)sum += 1.0 / i;
	printf("%.2f\n", sum);
	return 0;
}